For every \(\nu \in \mathfrak {M}^+\)  with \(\nu (\lbrace y\rbrace )=0\) , define the Kelvin transform
\(\nu ^*=\mathcal {K}_y\nu \in \mathfrak {M}^+\)  by means of the formula (see [1]})
\(d\nu ^*(x^*)=|x-y|^{\alpha -n}\,d\nu (x),\text{ \ where\ }x^*=J_y(x)\in \mathbb {R}^n.\) 
